1. Field of the Invention
This invention relates to image blur correction means for correcting image blur attributable to vibration applied to an image pickup apparatus on the basis of the result of the detection by vibration detecting means for detecting the state of the aforementioned vibration, and an image pickup apparatus having the image blur correction means.
The invention further relates to improvements in the image blur correction apparatus of a camera and an interchangeable lens with the image blur correction apparatus.
2. Related Background Art
In present-day cameras, operations important to photographing such as exposure determination and focusing, are all automated; therefore, even a person unskilled in camera operation has very little possibility of causing a failure in photographing.
Also, recently, a system for preventing hand vibration applied to a camera has been studied and factors for inducing an error in the photographing by a photographer have become almost null.
The system for preventing hand vibration will be briefly described here.
The hand vibration of a camera during photographing is usually vibration of a frequency of 1-12 Hz, but as a basic idea for enabling a photograph free of image blur to be taken even if such hand vibration is caused at a point of time when the shutter is released, the vibration of the camera by the above-mentioned hand vibration must be detected and a correction lens must be displaced in conformity with the detected value. Accordingly, to enable a photograph free of image blur to be taken even if the vibration of the camera is caused, firstly it is necessary to detect the vibration of the camera accurately, and secondly it is necessary to correct the displacement of the optical axis caused by the hand vibration.
Theoretically speaking, the detection of this vibration (camera vibration) can be effected by carrying on a camera a vibration sensor for detecting angular acceleration, angular velocity, angular displacement, etc., and means for electrically or mechanically integrating the output signal of the vibration sensor and outputting angular displacement. Then, a correction optical system for making a photographing optical axis eccentric is driven on the basis of this detected information and the suppression of image blur is effected.
Here, the epitome of a vibration preventing system using a vibration detecting apparatus will be described with reference to FIG. 10 of the accompanying drawings.
FIG. 10 shows a system for suppressing image blur attributable to camera pitch vibration 81p and to camera yaw vibration 81y, in the direction of arrows 81, and shows a case where an image blur correction apparatus is provided in the interchangeable lens of a single-lens reflex camera.
In FIG. 10, the reference numeral 82 designates a lens barrel, and the reference characters 89a, 89b, 89c and 89d denote photographing optical systems which form the image of an object, not shown, on an image plane 88. The reference characters 83p and 83y designate vibration detecting apparatus for detecting camera pitch vibration and camera yaw vibration, respectively, and their respective vibration detecting directions are indicated by 84p and 84y. The reference numeral 85 denotes a correction optical system (87p and 87y designate coils for giving thrust to the correction optical system 85, and 86p and 86y denote position detecting elements for detecting the position of the correction optical system 85), and the correction optical system 85 is provided with a position control loop, and is driven with the outputs of the vibration detecting apparatuses 83p and 83y as target values, and secures the stability on the image plane 88.
Also, although reduced in accuracy, the detection of the position of the correction optical system 85 is abolished to thereby reduce the cost, and vibration correction is also possible by an open control technique which does not provide the position control loop, but effects vibration correction control by only a vibration amount detected.
FIG. 11 of the accompanying drawings is an exploded perspective view showing an example of an image blur correction apparatus using the open control.
In FIG. 11, the reference numeral 1 designates a support frame for holding a correction lens, the reference numeral 2 denotes a ground plate for holding the support frame 1, the reference numeral 3 designates a first yoke which is a magnetic member fixed to the ground plate 2 by screws or the like, not shown, and the reference numeral 4 denotes a winding coil fixed to the support frame 1. The reference numeral 5 designates a second yoke which is a magnetic member fixed to the ground plate 2 by screws or the like, not shown, so as to sandwich the support frame 1 between it and the first yoke 3, the reference numeral 6 denotes two permanent magnets magnetically attracted and fixed to the second yoke 5 and provided with their positions deviated by about 90xc2x0 from each other. The reference characters 7a-7c designate shift pins each having one end thereof forced into the support frame 1 and the other end thereof inserted in a slot 2a formed in the ground plate 2, and radially provided about the optical axis at three locations equally divided into approximately 120xc2x0 about the optical axis. The reference characters 8a-8d denote springs for resiliently supporting the support frame 1 relative to the ground plate 2, and each of the springs 8a-8d has one end thereof positioned by a projection 1a provided on the support frame 1 and has the other end thereof positioned by a projection 2b provided on the ground plate 2, and the springs 8a-8d are provided at four locations equally divided into approximately 90xc2x0 about the optical axis. The projections 1a and the projections 2a radially protrude about the optical axis and are provided so as to be opposed to each other on the same straight line and thus, the springs 8 (8a, 8b, 8c, 8d) are also radially disposed about the optical axis.
The assembling procedure is such that the first yoke 3 is first fixed to the ground plate 2 with screws or the like inserted into the holes thereof. Next, projections provided on the bobbin, not shown, of the winding coil 4 are inserted into holes formed in the support frame 1, and the winding coil 4 is adhesively or otherwise fixed. Then, the shift pins 7 are forced into holes formed in the support frame 1 through the slots 2a formed in the ground plate 2. Thereby the support frame 1 has its movement in the direction of the optical axis regulated relative to the ground plate 2, but becomes movable except in the direction of the optical axis. Next, one end of each spring 8 is mounted on the projection 1a provided on the support frame 1 and the other end is mounted on the projection 2b provided on the ground plate 2. Thereby the support frame 1 is held substantially about the optical axis. Next, the permanent magnets 6 are magnetically attracted and fixed to the second yoke 5. Lastly, the second yoke 5 is fixed to the ground plate 2 by screws or the like so as to sandwich the support frame 1 between it and the first yoke 3.
The permanent magnets 6 and the winding coil 4 are disposed so as to be opposed to each other. Thereby a conventional closed magnetic circuit is formed between the first yoke 3 and the permanent magnets 6 because the second yoke 5 is a magnetic member, and the winding coil 4 provided in this closed magnetic circuit and fixed to the support frame 1 is electrically energized to thereby produce thrust and drive the support frame 1 by any stroke. Also, when the winding coil 4 is not electrically energized, the support frame 1 is held substantially at the central position by the springs 8, and since the springs 8 are provided at four locations equally divided into approximately 90xc2x0, the performance will not change even if the posture of the image blur correction apparatus changes.
The reference characters 9a and 9b designate vibration detecting sensors for detecting the vibration of an image pickup apparatus carrying the image blur correction apparatus thereon. The reference numeral 10 denotes a control circuit for effecting calculation on the basis of the outputs of the vibration detecting sensors 9a and 9b, and the control circuit 10 calculates the amount of driving of the support frame 1 (correction lens) so as to negate the vibration detected by the vibration detecting sensors 9a and 9b, and electrically energizes the winding coil 4 to thereby control the support frame 1 and secures the stability of the image plane.
In the above-described image blur correction apparatus of FIG. 11, the support frame 1 holding the correction lens is held by the springs 8 and when a shock is applied thereto, it resonates at a resonance frequency and by the spring constant of the springs 8, the resonance amplitude may become considerably great.
Also, when photographing is effected by the use of a single-lens reflex camera, mirror driving and shutter driving for the photographing operation are effected. If the shock by those drivings is applied to the aforedescribed vibration correction apparatus, the correction lens may resonate and adversely affect photographing.
The resonance amplitude attenuates with time after the shock has been applied and therefore, if the shutter time is long, the influence thereof is small, but if the shutter time becomes short, the influence thereof will become great.
Also, if the spring constant is made great, the resonance amplitude will become small, but during vibration correction, it is necessary to drive the correction lens against the springs and therefore, if the spring constant is made great, the consumed electric current will increase and thus, the spring constant cannot be made very great.
Also, depending on the camera on which the vibration correction apparatus is mounted, photographing can be accomplished without mirror driving and shutter driving being effected and therefore, it is necessary to optionally change the countermeasure for resonance in conformity with the camera on which the vibration correction apparatus is mounted.
It is a first object of the present invention to provide an image blur correction apparatus of which the central position of the blur correction is changed in conformity with the exposure time of a camera to reduce the influence of resonance attributable to the photographing operation of a correction lens held by resilient members such as springs upon the result of photographing and an image pickup apparatus having the image blur correction apparatus.
It is a second object of the present invention to provide an image blur correction apparatus of which the central position of the blur correction is changed in conformity with the focal length of a taking lens to reduce the influence of resonance attributable to the photographing operation of a correction lens held by resilient members such as springs upon the result of photographing and an image pickup apparatus having the image blur correction apparatus.
It is a third object of the present invention to provide an image blur correction apparatus of which the central position of the blur correction is changed in conformity with the exposure time of a camera or/and the focal length of a taking lens to reduce the influence of resonance attributable to the photographing operation of a correction lens held by resilient members such as springs upon the result of photographing and an image pickup apparatus having the image blur correction apparatus.
Further objects and constructions of the present invention will become apparent from the following description of some embodiments of the invention.